Variable valve timing control apparatus of internal combustion engine

ABSTRACT

A variable valve timing control apparatus of an internal combustion engine, has a housing having a plurality of shoes and a vane member having a plurality of vanes dividing each working fluid chamber formed between adjacent two shoes into advance and retard oil chambers. The vane member rotates to an advanced angle side and to a retarded angle side relative to the housing by selectively supplying or exhausting hydraulic pressure in or from the advance oil chamber and the retard oil chamber. A most-advanced angle position and a most-retarded angle position are limited by the fact that one vane touches one shoe from a circumferential direction. Radius of curvature of one of both corners of a base part of the one shoe, which is a corner located at a side where the one vane does not touch, is set to be greater than those of corners of the other shoes.

BACKGROUND OF THE INVENTION

The present invention relates to a variable valve timing control apparatus of an internal combustion engine, which variably controls open and closing timing of an intake valve and/or an exhaust valve of the engine in accordance with an engine operating condition.

As one of generally used variable valve timing control apparatuses, a vane type variable valve timing control apparatus disclosed in Japanese Patent Provisional Publication No. 2002-295212 (hereinafter is referred to as “JP2002-295212”) is known.

This vane type variable valve timing control apparatus has a housing to which a turning force is transmitted from an engine crankshaft and a vane member which is rotatably housed in the housing and is secured to an end portion of a camshaft. Further, a plurality of shoes are formed on an inner peripheral surface of the housing so as to protrude in a radially inward direction. Advance oil chambers and retard oil chambers are defined between a plurality of the shoes and a plurality of vanes of the vane member.

Hydraulic pressure discharged from an electric pump is selectively supplied to either one of the advance oil chamber and the retard oil chamber in accordance with an engine operating condition, and the vane member rotates in forward and reverse directions by this driving hydraulic pressure. The vane then touches the shoe from a circumferential direction, thereby limiting a most-advanced angle rotational position and a most-retarded angle rotational position. Open and closing timing of a timing sprocket intake valve is variably controlled in this manner in the vane type variable valve timing control apparatus.

SUMMARY OF THE INVENTION

In recent years, it has been required that a thickness in the circumferential direction of each shoe be as thin as possible, in order to increase the number of the vanes by a request to reduce the hydraulic pressure that is supplied to each chamber and in order to obtain a large relative rotational angle of the vane member with respect to the housing.

However, if the thickness of each shoe is formed thin, its strength decreases. Because of this, the shoe might be bent and deformed when the vane is pressed against the shoe from the circumferential direction, and there is a possibility that a desired relative rotational angle will not be obtained.

For this reason, to ensure the strength, there is no other way than to thicken the thickness of the shoe to some extent. However, there is a trade-off between an increase in the thickness of the shoe and an increase in the relative rotational angle between the housing and the vane. Thus, if the thickness of the shoe is thicken, it is difficult to obtain the large relative rotational angle between the housing and the vane.

It is therefore an object of the present invention to provide a variable valve timing control apparatus of the internal combustion engine, which is capable of ensuring the strength of the shoe while sufficiently securing the relative rotational angle between the housing and the vane member.

According to one aspect of the present invention, a variable valve timing control apparatus of an internal combustion engine, comprises: a cylindrical housing having, on an inner peripheral surface thereof, a plurality of shoes which protrude in a radially inward direction; and a vane member secured to a camshaft and having a plurality of vanes which divide each working fluid chamber formed between the adjacent two shoes into an advance oil chamber and a retard oil chamber, the vane member rotating to an advanced angle side and to a retarded angle side relative to the housing by selectively supplying or exhausting a hydraulic pressure in or from the advance oil chamber and the retard oil chamber, and a most-advanced angle rotational position and a most-retarded angle rotational position are limited by the fact that one certain vane touches one certain shoe from a circumferential direction with the one certain vane pressed against the one certain shoe, and radius of curvature of one of both corners of a base part of the one certain shoe, which is a corner located at a side where the one certain vane does not touch, is set to be greater than those of corners of the other shoes except the one certain shoe, in a structure in which the most-advanced angle rotational position or the most-retarded angle rotational position is limited with the one certain vane pressed against the one certain shoe.

According to another aspect of the present invention, a variable valve timing control apparatus of an internal combustion engine, comprises: a cylindrical housing having, on an inner peripheral surface thereof, a plurality of shoes which protrude in a radially inward direction; and a vane member secured to a camshaft and having a plurality of vanes which divide each working fluid chamber formed between the adjacent two shoes into an advance oil chamber and a retard oil chamber, the vane member rotating to an advanced angle side and to a retarded angle side relative to the housing by selectively supplying or exhausting a hydraulic pressure in or from the advance oil chamber and the retard oil chamber, and a most-advanced angle rotational position and a most-retarded angle rotational position are limited by the fact that one certain vane touches one certain shoe from a circumferential direction with the one certain vane pressed against the one certain shoe, and at least one of both corners of a base part of the one certain shoe which the one certain vane touches, which is a corner located at a side where the one certain vane does not touch, is provided with a thick portion, in a structure in which the most-advanced angle rotational position or the most-retarded angle rotational position is limited with the one certain vane pressed against the one certain shoe.

According to a further aspect of the invention, a variable valve timing control apparatus of an internal combustion engine, comprises: a cylindrical housing having, at an inner peripheral side of a main body thereof, a plurality of shoes which protrude in a radially inward direction; and a vane rotor secured to a camshaft and having a plurality of vanes which divide each working fluid chamber formed between the adjacent two shoes into an advance oil chamber and a retard oil chamber, the vane rotor rotating to an advanced angle side and to a retarded angle side relative to the housing by selectively supplying or exhausting a hydraulic pressure in or from the advance oil chamber and the retard oil chamber, and a most-advanced angle rotational position and a most-retarded angle rotational position are limited by the fact that one certain vane touches one certain shoe from a circumferential direction with the one certain vane pressed against the one certain shoe, and strength of the one certain shoe which the one certain vane touches is set to be greater than those of the other shoes which no vanes touch, in a structure in which the most-advanced angle rotational position or the most-retarded angle rotational position is limited with the one certain vane pressed against the one certain shoe.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exploded view of a variable valve timing control apparatus of a first embodiment of the present invention.

FIG. 2 is a schematic view showing a hydraulic circuit of the variable valve timing control apparatus.

FIG. 3 is a drawing showing a state in which a valve timing is controlled to a retard angle side.

FIG. 4 is a drawing showing a state in which the valve timing is controlled to an advance angle side.

FIG. 5 is a longitudinal cross section showing a lock state by a locking mechanism.

FIG. 6 is a drawing showing a state in which the valve timing is controlled to the retard angle side, of a second embodiment of the present invention.

FIG. 7 is a drawing showing a state in which the valve timing is controlled to the advance angle side, of the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, it is possible to ensure the strength of the shoe while sufficiently securing the relative rotational angle between the housing and the vane member.

Embodiments of a variable valve timing control apparatus of the present invention will now be explained below with reference to the drawings.

First Embodiment

FIGS. 1 to 5 show a first embodiment of the variable valve timing control apparatus. The variable valve timing control apparatus has a sprocket 1 that is driven and rotates by an engine crankshaft (not shown) through a timing chain, a camshaft 2 that is capable of rotating relative to the sprocket 1, a relative angular phase control mechanism (simply, a phase converter or a phase-change mechanism) 3 disposed between the sprocket 1 and the camshaft 2 and changing or controlling a relative rotational position between the sprocket 1 and the camshaft 2, and a hydraulic circuit 4 that actuates the phase-change mechanism 3.

The camshaft 2 is rotatably supported by a cylinder head (not shown) through a camshaft bearing. The camshaft 2 has a plurality of driving cams, each of which actuates an intake valve through a valve lifter. Each driving cam is formed integrally with the camshaft 2 at a certain position on an outer peripheral surface of the camshaft 2. Further, the camshaft 2 is provided with a female screw hole 2 b in an axial direction at an inner side of one end portion 2 a in order for a cam bolt 6 to screw in.

The phase-change mechanism 3 has a housing 5 arranged at the one end portion 2 a side of the camshaft 2, a vane member 7 secured to the one end portion 2 a of the camshaft 2 from the axial direction by the cam bolt 6 and relatively rotatably housed in the housing 5, four shoes 8 (first to fourth shoes 8 a to 8 d) formed on an inner peripheral surface of the housing 5, and four retard oil chambers 9 that are retard operating chambers and four advance oil chambers 10 that are advance operating chambers. As can be seen in FIGS. 3 and 4, the retard and advance oil chambers 9 and 10 are divided and defined by the first to fourth shoes 8 a to 8 d and after-mentioned four vanes 22 to 25 of the vane member 7.

The housing 5 has a substantially cylindrical shaped housing main body 11, a front plate (a second plate) 12 that closes a front side opening end of the housing main body 11, and a rear plate (a first plate) 13 that is also used as the sprocket 1 and closes a rear side opening end of the housing main body 11. These housing main body 11 and front plate 12 and rear plate 13 (sprocket 1) are tightened together in the axial direction by four bolts 14, then fixedly connected together.

The housing main body 11 is formed as a single-piece body by sintered metal material. The four shoes 8, i.e. the first to fourth shoes 8 a to 8 d, are formed integrally with the housing main body 11 so as to be arranged at almost regular intervals in a circumferential direction on the inner peripheral surface of the housing 5 and so as to protrude in a radially inward direction. Each of the first to fourth shoes 8 a to 8 d is formed relatively thin, and has a substantially same trapezoidal shape in cross section. A seal groove is formed on a top end part of the trapezoidal shape along the axial direction, and an almost square bracket (“]”)-shaped seal member 16 is fitted in the seal groove. Further, each shoe 8 is provided with a bolt insertion hole 17 at an outer circumferential side of the radial direction of the shoes 8 a to 8 d, i.e. at a base part side of the trapezoidal shape which is a connecting part to the housing main body 11. The insertion hole 17 opens in the axial direction, and each bolt 14 is inserted in the insertion hole 17.

Further, as can be seen in FIG. 1, for reduction in weight of the housing main body 11, substantially rectangular lightening portions 11 a are formed on an outer surface of the housing main body 11 where the shoes 8 a to 8 d are positioned.

In addition, with respect to the first shoe 8 a which the after-mentioned first vane 22 relatively rotates in a counterclockwise direction as shown in FIG. 3 and touches, as seen in FIGS. 1, 3 and 4, an R-shaped thick portion (a first thick portion) 18 a is formed integrally with the first shoe 8 a at one side of both corners in the circumferential direction of the base part, i.e. at a left side corner of the first shoe 8 a in FIG. 3.

An outer peripheral surface of this thick portion 18 a is formed into a substantially arc shape. More specifically, the outer peripheral surface of the thick portion 18 a has such gently curved shape (arc shape) that the outer peripheral surface gently curves from a rising portion of one side surface of the first shoe 8 a along an inner circumferential surface 11 b of the housing main body 11. Radius of curvature of this thick portion 18 a is set to be greater than those of R-shaped corners (e.g. reference signs 8 e in FIG. 3) of the other shoes 8 c and 8 d that are the shoes which the first vane 22 does not touch. With this setting, the strength of the base part of the first shoe 8 a increases as compared with the other shoes 8 c and 8 d.

On the other hand, at a right side corner (the base part) of the first shoe 8 a which the first vane 22 touches, a thick part 18 b is formed integrally with the first shoe 8 a. An outer surface of this thick part 18 b has a substantially flat inclined plane. The strength of the base part, at this thick part 18 b side, of the first shoe 8 a also increases.

With regard to the second shoe 8 b which the first vane 22 relatively rotates in a clockwise direction as shown in FIG. 4 and touches, as same as the first thick portion 18 a, a second thick portion 19 a is formed integrally with the second shoe 8 b at a corner (the base part) opposite to the other corner which the first vane 22 touches. Radius of curvature of this second thick portion 19 a is set to be greater than those of R-shaped corners 8 e of the other shoes 8 c and 8 d that are the shoes which the first vane 22 does not touch. With this setting, the strength of the base part of the second shoe 8 b increases as compared with the other shoes 8 c and 8 d.

On the other hand, at the other corner opposite to the second thick portion 19 a, a stepped rectangular protruding portion 19 b which the first vane 22 touches is formed integrally with the second shoe 8 b. Also by this protruding portion 19 b, the strength of the base part of the second shoe 8 b increases.

The front plate 12 is formed by pressing, and has a relatively thin disc shape. As shown in FIGS. 1 and 2, the front plate 12 is provided, in the middle thereof, with a large diameter opening 12 a into which the cam bolt 6 is inserted. Further, a semicircular positioning groove or notch 12 b is formed at a certain position on an outer peripheral surface of the front plate 12. Moreover, the front plate 12 is provided with four bolt insertion holes 12 c into which each bolt 14 is inserted, at regular intervals in a circumferential direction at an outer peripheral side of the front plate 12.

Whole of the rear plate 13 (the sprocket 1) is formed by sintered alloy, and has a high hardness by hear treatment when sintered. A plurality of teeth 1 a, where the timing chain is meshed and wound, are formed integrally with an outer circumferential portion of the rear plate 13.

Further, the rear plate 13 is provided, in the middle thereof, with a supporting opening 13 a for receiving and rotatably supporting the one end portion 2 a of the camshaft 2. Furthermore, the rear plate 13 is provided with female screw holes 13 b in order for a male screw of a top end of each bolt 14 to screw in, at regular intervals in a circumferential direction at an outer peripheral side of the rear plate 13.

The vane member 7 is formed as an integral part by metal material. The vane member 7 has a vane rotor 21 and the four vanes 22 to 25 (the first to fourth vanes 22 to 25). The vane rotor 21 is secured to the one end portion 2 a of the exhaust camshaft 2 from the axial direction by the cam bolt 6 with the cam bolt 6 inserted into an insertion hole 7 a that is formed in the middle of the vane member 7. The four vanes 22 to 25 are arranged at almost regular intervals in a circumferential direction of an outer circumferential surface of the vane rotor 21, and protrude in the radial direction.

The vane rotor 21 is rotatably supported by the seal member 16 fitted in the seal groove on an upper surface of the top end part of each of the shoes 8 a to 8 d while making sliding contact with the seal member 16. As shown in FIGS. 1 and 3, four retard side oil paths 27 that communicate with the respective retard oil chambers 9 and four advance side oil paths 28 that communicate with the respective advance oil chambers 10 are provided in the radial direction at both sides of each of the vanes 22 to 25. Further, as shown in FIG. 2, the vane rotor 21 has a fitting groove 21 a in which the top end part of the one end portion 2 a of the camshaft 2 is fitted, in the middle of an end surface at the camshaft 2 side of the vane rotor 21.

As shown in FIG. 3, each of the vanes 22 to 25 is placed between the adjacent two shoes of the shoes 8 a to 8 d. A seal groove is formed on a top end surface of each vane along the axial direction, and an almost square bracket (“]”)-shaped seal member 20 that makes sliding contact with the inner circumferential surface 11 b of the housing main body 11 is fitted in the seal groove.

As can be seen in FIGS. 3 and 4, the first vane 22 has a largest width (a maximum width) as compared with the other vanes 23 to 25. The other three vanes 23 to 25 have a substantially same width, and its width is set to be much smaller than the width of the first vane 22. By setting the width of the three vanes 23 to 25 to be smaller than the first vane 22 in this manner, good weight balance of the whole of the vane member 7 can be achieved.

The first vane 22 limits a relative rotational position of a most-retarded angle side of the vane member 7 with respect to the housing 5 by the fact that one side surface of the first vane 22 of the vane member 7 touches an opposing side surface of the first shoe 8 a when the vane member 7 rotates to the maximum in the counterclockwise direction as shown in FIG. 3. On the other hand, the first vane 22 limits the relative rotational position of a most-advanced angle side of the vane member 7 with respect to the housing 5 by the fact that the other side surface of the first vane 22 of the vane member 7 touches an opposing side surface of the second shoe 8 b when the vane member 7 rotates to the maximum in the clockwise direction as shown in FIG. 4.

The first vane 22 has, on an outer peripheral surface thereof, a cutting portion 22 a which faces the thick part 18 b of the first shoe 8 a. This cutting portion 22 a is formed into an arc shape along the substantially flat outer surface of the thick part 18 b. More specifically, the cutting portion 22 a is formed so that when the vane member 7 rotates to the maximum in the counterclockwise direction as shown in FIG. 3, the cutting portion 22 a faces the thick part 18 b with a slight gap appearing between the outer side surface of the thick part 18 b and the cutting portion 22 a.

In addition, a protrusion 22 b is formed integrally with the first vane 22 at an opposite side in the circumferential direction to the cutting portion 22 a. The seal groove in which the above-mentioned seal member 20 is fitted is formed on an outer surface of this protrusion 22 b. As shown in FIG. 4, the protrusion 22 b limits the maximum rotation in the clockwise direction of the vane member 7 by the fact that an outer side surface in the circumferential direction of the protrusion 22 b touches the protruding portion 19 b of the second shoe 8 b from the circumferential direction.

Here, an arrangement of the shoes 8 a to 8 d and the vanes 22 to 25 is designed so that, in the state in which the first vane 22 touches the first shoe 8 a and the second shoe 8 b as shown in FIGS. 3 and 4 respectively, the other vanes 23 to 25 do not touch any of the shoes 8 a to 8 d which the other vanes 23 to 25 face in the circumferential direction when rotating.

Further, a locking mechanism that restrains free rotation of the vane member 7 is provided between the first vane 22 and the rear plate 13.

As shown in the drawings (especially in FIG. 5), the locking mechanism has a lock pin 30 slidably housed or held in a sliding hole 29 that is formed at and penetrates the first vane 22 in the axial direction and freely moving toward or away from the rear plate 13 side, a cup-shaped locking hole unit 31 fixed in a retaining hole that is formed at a substantially middle position in a radial direction of the rear plate 13, a locking hole 31 a formed in the locking hole unit 31 and locking the vane member 7 by receiving and engaging with a top end portion 30 a of the lock pin 30, and a locking/releasing mechanism engaging and disengaging the top end portion 30 a of the lock pin 30 with and from the locking hole 31 a in accordance with an engine start condition.

An inner peripheral surface of the sliding hole 29 is formed into a step shape, then the sliding hole 29 has a small diameter hole at a top end side and a large diameter hole at a rear end side. An annular stepped portion 29 a is formed between these small diameter hole and large diameter hole.

As for the lock pin 30, as shown in FIGS. 1 and 5, an outer peripheral surface of the lock pin 30 is formed into a step shape to fit to the step shape of the sliding hole 29, then the lock pin 30 has a small diameter portion 30 b at a top end side and a large diameter portion 30 c at a rear end side. A stepped portion 30 d is formed between these small diameter portion 30 b and large diameter portion 30 c. The top end portion 30 a of the small diameter portion 30 b is a solid portion, and this outer peripheral surface is formed into a conical shape, which can easily engages with the locking hole 31 a from the axial direction. Between the stepped portion 29 a of the sliding hole 29 and the stepped portion 30 d of the lock pin 30, an annular pressure-receiving chamber or space 35 is formed.

The locking hole 31 a has a bottom, and is positioned, in the circumferential direction, at the advance oil chamber 10 side (the retard side of the vane member 7).

This position is set so that when the lock pin 30 is engaged, the relative rotational angle between the housing 5 and the vane member 7 becomes an optimum conversion angle for the engine start.

Here, a rectangular cutting groove (not shown) is provided on an inner surface of the front plate 12 at the rear end side of the sliding hole 29. This cutting groove communicates with the outside air, thereby ensuring good sliding movement of the lock pin 30 all the time within a rotation range of the vane member 7.

The locking/releasing mechanism is provided between a rear end portion of the lock pin 30 and an inner end surface of the front plate 12. The locking/releasing mechanism has a coil spring 32 that forces the lock pin 30 in a forward direction (in an engagement direction), and a lock cancelling hydraulic circuit (not shown) that supplies a hydraulic pressure to the locking hole 31 a and the pressure-receiving space 35 to move the lock pin 30 in a backward direction (in a disengagement direction). This lock cancelling hydraulic circuit is configured so that, as shown in FIGS. 3 to 5, a hydraulic pressure selectively supplied to the retard oil chamber 9 and the advance oil chamber 10 is supplied to and discharged from the pressure-receiving space 35 and the locking hole 31 a through oil passages 42 a and 42 b that are formed at an inside and on the side surface of the first vane 22.

Further, a positioning means or mechanism is provided between the housing main body 11 and the rear plate 13. The positioning mechanism performs the function of fixing rotational positions of the housing main body 11 and the rear plate 13, i.e. positions in the circumferential direction of the top end portion 30 a of the lock pin 30 and the locking hole 31 a, when assembling each component by the bolts 14.

The positioning mechanism has, as shown in FIGS. 1, 3 and 4, a recessed portion (a positioning recessed portion) 33 that is formed at a certain position of an outer circumferential edge, at the rear plate 13 side, of the housing main body 11 (the first shoe 8 a) by a cutting process, and a positioning pin (a positioning protrusion) 34 that is formed at a certain position of an inner end surface at an outer circumferential part side of the rear plate 13, which corresponds to the position of the recessed portion 33.

The recessed portion 33 has a two-step shape along the radial direction by cutting the outer surface at the thick part 18 b side of the housing main body 11. This two-step shape (two-step groove) is formed so as to penetrate the outer circumferential edge of the housing main body 11 from the inner end surface side of the rear plate 13 in the axial direction. The recessed portion 33 is formed at the same time as a sintering mold of the housing main body 11.

A width of a deepest groove of the recessed portion 33 is set to be slightly smaller than an outside diameter of the positioning pin 34. A depth of this deepest groove is set to be slightly larger than the outside diameter of the positioning pin 34. These width and depth are set so that the housing main body 11 and the rear plate 13 do not rattle in the circumferential direction with the positioning pin 34 inserted and fitted.

Thus the deepest groove of the recessed portion 33 has the function of fixing a radial and circumferential position of the rear plate 13 relative to the housing main body 11 with the positioning pin 34 previously inserted and engaged from the axial direction when tightening and connecting the housing main body 11, the front plate 12 and the rear plate 13 together by the bolts 14.

A base end portion of the positioning pin 34 is press-fitted in a pin hole that is formed and penetrates the rear plate 13 in the axial direction in a position close to the locking hole 31 a at the outer circumferential part side of the rear plate 13, which corresponds to the position of the deepest groove of the recessed portion 33. A top end portion of the positioning pin 34 protrudes in the direction of the housing main body 11, then is inserted in and engaged with the deepest groove of the recessed portion 33 from the axial direction.

The hydraulic circuit 4 selectively supplies the hydraulic pressure in each of the retard and advance oil chambers 9 and 10 or exhausts the oil supplied in the retard and advance oil chambers 9 and 10. As shown in FIG. 2, the hydraulic circuit 4 has a retard side oil passage 36 that communicates with each retard side oil path 27, an advance side oil passage 37 that communicates with each advance side oil path 28, an oil pump 39 that selectively supplies the hydraulic pressure in the oil passages 36 and 37 through an electromagnetic switching valve 38, and an oil drain passage 40 that selectively communicates with the oil passages 36 and 37 through the electromagnetic switching valve 38.

The retard side oil passage 36 communicates with the retard side oil path 27 through an oil passage 36 a and a groove 36 b which are formed inside the camshaft 2 in the radial direction and in the axial direction respectively. The advance side oil passage 37 communicates with the advance side oil path 28 through an oil passage 37 a and a groove 37 b which are formed inside the camshaft 2 in the radial direction and in the axial direction respectively.

The electromagnetic switching valve 38 is a two-way valve, and selectively switches the retard and advance side oil passages 36 and 37, an oil discharge passage 39 a of the oil pump 39 and the oil drain passage 40 by an output signal from a controller (not shown).

The controller has a computer, and inputs information signal from sensors such as a crank angle sensor, an airflow meter, an engine temperature sensor and a throttle valve opening sensor (all not shown), and detects a current engine operating condition. Further, the controller outputs a control pulse current to an electromagnetic coil of the electromagnetic switching valve 38 in accordance with the engine operating condition.

Here, operation of the present embodiment will be explained.

First, upon the engine start, as shown in FIGS. 3 and 5, the top end portion 30 a of the lock pin 30 is previously inserted in and engaged with the locking hole 31 a, and the position of the vane member 7 is restrained in an optimum position for the engine start. Therefore, when turning an ignition on and starting to crank the engine, good engine startability can be ensured by the smooth cranking.

When the engine operating condition is in a low rotation speed low load region after the engine start, the controller maintains no current application to the electromagnetic coil of the electromagnetic switching valve 38. With this operation, the oil discharge passage 39 a of the oil pump 39 and the advance side oil passage 37 are connected to each other, and the retard side oil passage 36 and the oil drain passage 40 are connected to each other.

Thus, working fluid (the oil) discharged from the oil pump 39 flows into each advance oil chamber 10 through the advance side oil passage 37, then each advance oil chamber 10 becomes a high pressure. On the other hand, the working fluid in the retard oil chamber 9 is exhausted in an oil pan 41 from the oil drain passage 40 through the retard side oil passage 36, then each retard oil chamber 9 becomes a low pressure.

At this time, the working fluid flowing into each advance oil chamber 10 is supplied to the locking hole 31 a from the oil passage 42 a, and an inside of the locking hole 31 a becomes the high pressure. The lock pin 30 then moves in the backward direction and the top end portion 30 a comes out of the locking hole 31 a (the top end portion 30 a is disengaged with the locking hole 31 a), thereby allowing the free rotation of the vane member 7.

When the vane member 7 rotates in the clockwise direction as shown in FIG. 4 with increase or expansion of volume of the advance oil chamber 10, the protrusion 22 b of the first vane 22 touches (or is pressed against) the protruding portion 19 b of the second shoe 8 b, a further rotation in the clockwise direction is then limited. With this operation and working, the relative rotational angle (a relative rotational phase) of the camshaft 2 (the vane member 7) with respect to the sprocket 1 (the rear plate 13) is converted to the most-advanced angle side. As a consequence, a stable engine rotation can be ensured, also engine combustion efficiency can be improved.

Next, when the engine operating condition is in a high rotation speed high load region, the controller outputs the control current to the electromagnetic switching valve 38, and the oil discharge passage 39 a and the retard side oil passage 36 are connected to each other, also the advance side oil passage 37 and the oil drain passage 40 are connected to each other. With this operation, the working fluid in the advance oil chamber 10 is exhausted in the oil pan 41, then each advance oil chamber 10 becomes the low pressure. On the other hand, the working fluid is supplied to the retard oil chamber 9, then the retard oil chamber 9 becomes the high pressure. At this time, since the working fluid (the hydraulic pressure) is supplied to the pressure-receiving space 35 from the retard oil chamber 9 through the oil passage 42 b, the disengagement state in which the lock pin 30 comes out of the locking hole 31 a is maintained.

When the vane member 7 rotates with respect to the housing 5 in the counterclockwise direction as shown in FIG. 3, the one side surface at the cutting portion 22 a side of the first vane 22 of the vane member 7 touches (or is pressed against) the opposing side surface of the first shoe 8 a, a further rotation in the counterclockwise direction is then limited. With this operation and working, the relative rotational angle (the relative rotational phase) of the camshaft 2 (the vane member 7) with respect to the sprocket 1 (the rear plate 13) is converted to the most-retarded angle side. As a consequence, open and closing timing of the intake valve is controlled to the most-retarded angle side, and an output of the engine in the high rotation speed high load region can be increased.

Further, just before an engine stop, the working fluid (the hydraulic pressure) is exhausted in the oil pan 41 from each of the retard and advance oil chambers 9 and 10 through the oil drain passage 40, and the hydraulic pressure in the pressure-receiving space 35 and the locking hole 31 a also decreases. As a result, the vane member 7 relatively rotates to the retarded angle side by an alternating torque that acts on the exhaust camshaft 2, then when the vane member 7 is positioned at a predetermined rotational position, the lock pin 30 moves in the forward direction by the spring force of the coil spring 32, and the top end portion 30 a is engaged with the locking hole 31 a.

In this case, since exact positioning, in the circumferential direction, of the lock pin 30, the locking hole 31 a and the housing 5 is achieved when assembling each component, smooth engagement of the lock pin 30 can be ensured.

That is, in the assembly of each component, when connecting the front plate 12 and the rear plate 13 to the housing main body 11 by the bolts 14, the front plate 12 is temporarily connected to a front end side of the housing main body 11 by the bolts 14. At the same time, the positioning pin 34 is inserted in and engaged with the deepest groove of the positioning recessed portion 33 of the housing main body 11 from the axial direction while fitting the rear plate 13 to a rear end side of the housing main body 11.

At this time, the top end portion 30 a of the lock pin 30 is engaged with the locking hole 31 a of the rear plate 13 with the lock pin 30 and the coil spring 32 inserted and housed in the sliding hole 29.

Subsequently, the male screw of the top end of each bolt 14 screws in the respective female screw hole 13 b of the rear plate 13 and each bolt 14 is tightened, thereby tightly connecting both front and rear plates 12 and 13 to the housing main body 11. Also the positioning of the rear plate 13 in the circumferential direction with respect to the housing main body 11 can be ensured.

Accordingly, even if there occurs misalignment between each bolt 14 and the respective bolt insertion hole 17 of the housing main body 11, it is possible to surely fix the position, in the circumferential direction, of the housing with respect to the top end portion 30 a of the lock pin 30 and the locking hole 31 a of the rear plate 13.

Further, in this embodiment, since the first thick portion 18 a and the second thick portion 19 a are formed at the respective corners of the first shoe 8 a and the second shoe 8 b opposite to the other corners which the first vane 22 of the vane member 7 touches (or opposite to the other corners against which the first vane 22 of the vane member 7 is pressed), the strength of the both shoes 8 a and 8 b, especially, the strength of the base parts of the shoes 8 a and 8 b, can be greatly increased.

With this structure, thicknesses of the first and second shoes 8 a and 8 b can be set to be as thin as possible. As a consequence, the relative rotational angle of the vane member 7 with respect to the housing 5 can be large.

Furthermore, the first vane 22 is provided, at one side portion on the outer peripheral surface thereof, with the arc shaped cutting portion 22 a. Therefore, this leads to reduction in weight of the vane member 7. Also, a plurality of the lightening portions 11 a are formed in the housing main body 11. This also leads to reduction in weight of the housing main body 11.

In addition, since the protrusion 22 b is formed at the opposite side to the cutting portion 22 a of the first vane 22 and the seal groove is formed at this protrusion 22 b, the effective use of the protrusion 22 b can be made.

Moreover, since the protruding portion 19 b is provided at one side portion of the second shoe 8 b and the outer surface of the above protrusion 22 b touches this protruding portion 19 b, the strength of the second shoe 8 b can be further increased in combination with the second thick portion 19 a.

Additionally, the locking hole 31 a is not directly formed on the rear plate 13, but formed using the locking hole unit 31. Thus, a thickness of the rear plate 13 can be adequately thin while securing a depth of the locking hole 31 a. Consequently, it is possible to reduce the weight of the apparatus and shorten a length in the axial direction of the apparatus, and this facilitates installation of the apparatus in an engine room.

Second Embodiment

FIGS. 6 and 7 show a second embodiment of the variable valve timing control apparatus. A basic structure is the same as that of the first embodiment. However, in the second embodiment, the relative rotational position of the most-advanced angle side of the vane member 7 is limited by the fact that, as shown in FIG. 7, the narrow second vane 23, which is adjacent to the first vane 22 in the counterclockwise direction, touches a side surface at the thick portion 18 a side of the first shoe 8 a when the vane member 7 rotates to the maximum to the most-advanced angle side (i.e. in the clockwise direction) with respect to the housing 5.

That is, as same as the first embodiment, the first shoe 8 a is provided with the first thick portion 18 a and the thick part 18 b at the both corners of the first shoe 8 a.

On the other hand, as for the second vane 23, a protruding portion 62 is formed integrally with a base portion side surface, at the first shoe 8 a side, of the second vane 23. This protruding portion 62 is a protrusion having a rectangular stepped shape. As shown in the drawings, an outer surface 62 a has such tapered shape that the outer surface 62 a fits to a shape of a tapered side surface of the first thick portion 18 a of the first shoe 8 a.

Here, the protrusion 22 b of the first vane 22 and the protruding portion 19 b of the second shoe 8 b in the first embodiment could be removed in the second embodiment. The other configuration is the same as the first embodiment. For instance, radius of curvature of each of the both corners 8 e of the shoes 8 b to 8 d is set to be smaller than that of the corner of the first thick portion 18 a of the first shoe 8 a.

According to this embodiment, as shown in FIG. 6, when the vane member 7 relatively rotates with respect to the housing 5 in the counterclockwise direction in accordance with the engine operating condition, the one side surface of the first vane 22 of the vane member 7 touches (or is pressed against) the opposing side surface of the first shoe 8 a, a further rotation in the counterclockwise direction is then limited. With this operation and working, the relative rotational angle (the relative rotational phase) of the camshaft 2 (the vane member 7) with respect to the sprocket 1 (the rear plate 13) is converted to the most-retarded angle side.

On the other hand, as shown in FIG. 7, when the vane member 7 relatively rotates with respect to the housing 5 in the clockwise direction, the outer surface 62 a of the protruding portion 62 of the second vane 23 touches (or is pressed against) the opposing side surface of the first shoe 8 a, a further rotation in the clockwise direction is then limited. With this operation and working, the relative rotational angle (the relative rotational phase) of the camshaft 2 (the vane member 7) with respect to the sprocket 1 (the rear plate 13) is converted to the most-advanced angle side.

As described above, in the second embodiment, such working that the first vane 22 touches the first shoe 8 a upon the conversion to the most-retarded angle side is the same as the first embodiment. However, upon the conversion to the most-advanced angle side, the protruding outer surface 62 a of the second vane 23 touches the opposing side surface of the first shoe 8 a.

At this time, since the strength of the both corners of the first shoe 8 a increases by the first thick portion 18 a and the thick part 18 b, it is possible to suppress bend or deformation of the first shoe 8 a when the second vane 23 is pressed against the first shoe 8 a and when the first vane 22 is pressed against the first shoe 8 a.

On the other hand, the strength of the base portion of the second vane 23 also increases by the protruding portion 62. Thus, it is possible to adequately suppress bend or deformation, in a direction opposite to a pressing direction, of the second vane 23 when the outer surface 62 a of the second vane 23 is pressed against the first shoe 8 a.

As a consequence, by each high strength of the first shoe 8 a and the second vane 23, the desired maximum rotational phase of the vane member 7 relative to the housing 5 can be obtained all the time.

Further, since the protruding outer surface 62 a of the second vane 23 is formed into the tapered shape as same as the opposing side surface of the first shoe 8 a, a stable contact state of these both surfaces can be obtained. The other effects of the second embodiment are the same as the first embodiment.

From the foregoing, the present invention includes the following structure or configuration of the variable valve timing control apparatus, and has the following effects.

(a) In the variable valve timing control apparatus, radius of curvature of one of both corners of a base part of the one certain shoe, which is a corner located at a side where the one certain vane does not touch, is set to be greater than those of corners of the other shoes except the one certain shoe, in a structure in which the most-advanced angle rotational position and the most-retarded angle rotational position are limited with the one certain vane pressed against the one certain shoe. (b) In the variable valve timing control apparatus, the vane member is configured so that one of a plurality of the vanes is thicker, in the circumferential direction, than the other vanes and the thicker one vane touches at least one of two shoes which are adjacent to each other in the circumferential direction of the thicker one vane. And radius of curvature of one of both corners of a base part of the one shoe which the thicker one vane touches, which is a corner located at a side where the thicker one vane does not touch, is set to be greater than those of corners of the other shoes which the thicker one vane does not touch. (c) In the variable valve timing control apparatus, the thicker one vane is provided with a lock pin that can protrude and retract in a rotation axis direction of the camshaft. The housing is provided with a locking hole that receives therein the lock pin. And a relative rotation of the vane member with respect to the housing is limited by the fact that the lock pin protrudes and engages with the locking hole in accordance with an engine operating condition. (d) In the variable valve timing control apparatus, an outer peripheral surface of the lock pin is circular in cross section. The thicker one vane provided with the lock pin has an arc cutting portion at at least one side in the circumferential direction on an outer peripheral surface of the thicker one vane. And a thick part is formed at a base part side corner of the shoe which is an opposite side to the cutting portion. (e) In the variable valve timing control apparatus, the shoe, against which a side of the cutting portion of the thicker one vane provided with the lock pin is pressed, touches the thicker one vane at one side surface of an inner peripheral side of the shoe. And radius of curvature of one of both corners of a base part of the shoe, which is a corner located at a side where the thicker one vane does not touch, is set to be greater than those of corners of the other shoes except the one certain shoe. (f) In the variable valve timing control apparatus, each of the vanes has, on a top end surface thereof, a seal member that makes sliding contact with an inner circumferential surface of the housing. And the thicker one vane is provided with not the cutting portion but the seal member at the other side in the circumferential direction on the outer peripheral surface of the thicker one vane. (g) In the variable valve timing control apparatus, the housing has a cylindrical shaped housing main body having both opening ends in an axial direction, a first plate closing one of the both opening ends of the housing main body and having the locking hole, and a second plate closing the other opening end of the housing main body. And a positioning mechanism, which performs a function of fixing rotational positions in the circumferential direction of the housing main body and the first plate, is provided at the thick part of the shoe which is the opposite side to the cutting portion of the thicker one vane. (h) In the variable valve timing control apparatus, the positioning mechanism has a positioning recessed portion formed at the shoe and a positioning protrusion formed at the first plate. And the positioning between the housing main body and the first plate is made by inserting the positioning protrusion in the positioning recessed portion. (i) In the variable valve timing control apparatus, the housing has a cylindrical shaped housing main body having both opening ends in an axial direction and a pair of plates closing the both opening ends of the housing main body. And each of the shoes has a bolt insertion hole into which a bolt is inserted in a rotation axis direction of the camshaft for fixedly connecting the housing main body and a pair of the plates together. (j) In the variable valve timing control apparatus, when the rotation of the vane member relative to the housing is limited to the most-advanced angle rotational position or the most-retarded angle rotational position, the one certain vane touches the base part of the one certain shoe which is located at an outer peripheral side of the one certain shoe.

According to the above variable valve timing control apparatus, a position of the one certain shoe where the vane touches is the base part of the one certain shoe located at the outer peripheral side of the one certain shoe, i.e. at a connecting portion to the housing main body of the housing which has high rigidity. Thus, bend or deformation of the one certain shoe due to the press by the vane can be suppressed.

(k) In the variable valve timing control apparatus, one of a plurality of the vanes is provided with a lock pin whose outer peripheral surface is circular in cross section and which can move forward and backward in a rotation axis direction of the camshaft. The housing is provided with a locking hole that receives therein the lock pin. A relative rotation of the vane member with respect to the housing is limited by the fact that the lock pin protrudes and engages with the locking hole in accordance with an engine operating condition. The vane provided with the lock pin has an arc cutting portion at at least one side in the circumferential direction on an outer peripheral surface of the vane. A thick part is formed at the shoe which is an opposite side to the cutting portion. The thick portion is formed at both corners of a base part of the shoe which the vane touches. And the vane touches both sides in the circumferential direction of the shoe.

The entire contents of Japanese Patent Application No. 2011-104882 filed on May 10, 2011 are incorporated herein by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A variable valve timing control apparatus of an internal combustion engine, comprising: a cylindrical housing having, on an inner peripheral surface thereof, a plurality of shoes which protrude in a radially inward direction; and a vane member secured to a camshaft and having a plurality of vanes which divide each working fluid chamber formed between the adjacent two shoes into an advance oil chamber and a retard oil chamber, the vane member rotating to an advanced angle side and to a retarded angle side relative to the housing by selectively supplying or exhausting a hydraulic pressure in or from the advance oil chamber and the retard oil chamber, and a most-advanced angle rotational position and a most-retarded angle rotational position being limited by the fact that one certain vane touches one certain shoe from a circumferential direction with the one certain vane pressed against the one certain shoe, and radius of curvature of one of both corners of a base part of the one certain shoe, which is a corner located at a side where the one certain vane does not touch, being set to be greater than those of corners of the other shoes except the one certain shoe, in a structure in which the most-advanced angle rotational position or the most-retarded angle rotational position is limited with the one certain vane pressed against the one certain shoe.
 2. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 1, wherein: radius of curvature of one of both corners of a base part of the one certain shoe, which is a corner located at a side where the one certain vane does not touch, is set to be greater than those of corners of the other shoes except the one certain shoe, in a structure in which the most-advanced angle rotational position and the most-retarded angle rotational position are limited with the one certain vane pressed against the one certain shoe.
 3. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 1, wherein: the vane member is configured so that one of a plurality of the vanes is thicker, in the circumferential direction, than the other vanes and the thicker one vane touches at least one of two shoes which are adjacent to each other in the circumferential direction of the thicker one vane, and radius of curvature of one of both corners of a base part of the one shoe which the thicker one vane touches, which is a corner located at a side where the thicker one vane does not touch, is set to be greater than those of corners of the other shoes which the thicker one vane does not touch.
 4. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 3, wherein: the thicker one vane is provided with a lock pin that can protrude and retract in a rotation axis direction of the camshaft, the housing is provided with a locking hole that receives therein the lock pin, and a relative rotation of the vane member with respect to the housing is limited by the fact that the lock pin protrudes and engages with the locking hole in accordance with an engine operating condition.
 5. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 4, wherein: an outer peripheral surface of the lock pin is circular in cross section, the thicker one vane provided with the lock pin has an arc cutting portion at at least one side in the circumferential direction on an outer peripheral surface of the thicker one vane, and a thick part is formed at a base part side corner of the shoe which is an opposite side to the cutting portion.
 6. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 5, wherein: the shoe, against which a side of the cutting portion of the thicker one vane provided with the lock pin is pressed, touches the thicker one vane at one side surface of an inner peripheral side of the shoe, and radius of curvature of one of both corners of a base part of the shoe, which is a corner located at a side where the thicker one vane does not touch, is set to be greater than those of corners of the other shoes except the one certain shoe.
 7. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 5, wherein: each of the vanes has, on a top end surface thereof, a seal member that makes sliding contact with an inner circumferential surface of the housing, and the thicker one vane is provided with not the cutting portion but the seal member at the other side in the circumferential direction on the outer peripheral surface of the thicker one vane.
 8. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 5, wherein: the housing has a cylindrical shaped housing main body having both opening ends in an axial direction, a first plate closing one of the both opening ends of the housing main body and having the locking hole, and a second plate closing the other opening end of the housing main body, and a positioning mechanism, which performs a function of fixing rotational positions in the circumferential direction of the housing main body and the first plate, is provided at the thick part of the shoe which is the opposite side to the cutting portion of the thicker one vane.
 9. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 8, wherein: the positioning mechanism has a positioning recessed portion formed at the shoe and a positioning protrusion formed at the first plate, and the positioning between the housing main body and the first plate is made by inserting the positioning protrusion in the positioning recessed portion.
 10. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 1, wherein: the housing has a cylindrical shaped housing main body having both opening ends in an axial direction and a pair of plates closing the both opening ends of the housing main body, and each of the shoes has a bolt insertion hole into which a bolt is inserted in a rotation axis direction of the camshaft for fixedly connecting the housing main body and a pair of the plates together.
 11. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 1, wherein: when the rotation of the vane member relative to the housing is limited to the most-advanced angle rotational position or the most-retarded angle rotational position, the one certain vane touches the base part of the one certain shoe which is located at an outer peripheral side of the one certain shoe.
 12. A variable valve timing control apparatus of an internal combustion engine, comprising: a cylindrical housing having, on an inner peripheral surface thereof, a plurality of shoes which protrude in a radially inward direction; and a vane member secured to a camshaft and having a plurality of vanes which divide each working fluid chamber formed between the adjacent two shoes into an advance oil chamber and a retard oil chamber, the vane member rotating to an advanced angle side and to a retarded angle side relative to the housing by selectively supplying or exhausting a hydraulic pressure in or from the advance oil chamber and the retard oil chamber, and a most-advanced angle rotational position and a most-retarded angle rotational position being limited by the fact that one certain vane touches one certain shoe from a circumferential direction with the one certain vane pressed against the one certain shoe, and at least one of both corners of a base part of the one certain shoe which the one certain vane touches, which is a corner located at a side where the one certain vane does not touch, being provided with a thick portion, in a structure in which the most-advanced angle rotational position or the most-retarded angle rotational position is limited with the one certain vane pressed against the one certain shoe.
 13. The variable valve timing control apparatus of the internal combustion engine as claimed in claim 12, wherein: one of a plurality of the vanes is provided with a lock pin whose outer peripheral surface is circular in cross section and which can move forward and backward in a rotation axis direction of the camshaft, the housing is provided with a locking hole that receives therein the lock pin, a relative rotation of the vane member with respect to the housing is limited by the fact that the lock pin protrudes and engages with the locking hole in accordance with an engine operating condition, the vane provided with the lock pin has an arc cutting portion at at least one side in the circumferential direction on an outer peripheral surface of the vane, a thick part is formed at the shoe which is an opposite side to the cutting portion, the thick portion is formed at both corners of a base part of the shoe which the vane touches, and the vane touches both sides in the circumferential direction of the shoe.
 14. A variable valve timing control apparatus of an internal combustion engine, comprising: a cylindrical housing having, at an inner peripheral side of a main body thereof, a plurality of shoes which protrude in a radially inward direction; and a vane rotor secured to a camshaft and having a plurality of vanes which divide each working fluid chamber formed between the adjacent two shoes into an advance oil chamber and a retard oil chamber, the vane rotor rotating to an advanced angle side and to a retarded angle side relative to the housing by selectively supplying or exhausting a hydraulic pressure in or from the advance oil chamber and the retard oil chamber, and a most-advanced angle rotational position and a most-retarded angle rotational position being limited by the fact that one certain vane touches one certain shoe from a circumferential direction with the one certain vane pressed against the one certain shoe, and strength of the one certain shoe which the one certain vane touches being set to be greater than those of the other shoes which no vanes touch, in a structure in which the most-advanced angle rotational position or the most-retarded angle rotational position is limited with the one certain vane pressed against the one certain shoe. 